It applies quite particularly, although not exclusively, to devices, like the one described in document FR 2 733 176, in which each mold half consists of a mold holder, of a shell holder fixed to the mold holder and of a shell supported by the shell holder, the cavity portions of each mold half being made in said shells. It of course applies to devices anterior to the one described in this document FR-2 733 176, that is to say to devices in which the mold holders do not support a shell holder to which a shell is fixed, but each support a one-piece component containing not only the cavity portion of the mold half, but also tubing for regulating the temperature of the mold.
FIG. 1A schematically illustrates, in axial half section and in lateral perspective from above, a mold, denoted in its entirety by the reference 1, of a molding device as described and depicted for example in document FR-2 733 176, to which the invention can apply. The mold 1, of axis 7, comprises two mold halves 2A, 2B respectively, able to move one relative to the other, particularly in rotation (arrow 3A, 3B, respectively) about a fixed common axis 4, and a mold base 5 which can move with respect to the two mold halves 2A, 2B in axial translation coaxial to the axis 7 (arrow 6).
Each mold half 2A, 2B comprises a mold holder 8A, 8B, respectively, which is equipped with respective support arms 15A, 15B articulated to the aforementioned axle 4, a respective shell holder 9A, 9B fixed to the corresponding mold holder in any way known to those skilled in the art, and a respective shell 10A, 10B supported by respective shell holder 9A, 9B in any way known to those skilled in the art. The two shells 10A, 10B and the mold base 5 comprise respective molding cavity portions 11A, 11B and 12 which, when the mold is in the closed position, together define a molding cavity 13 which is coaxial with the axis 7 of the mold 1.
Along the collaborating respective peripheries of the half shells 10A, 10B and of the base 5, the half shells have respective grooves 14A, 14B and the base has a radially projecting peripheral rib 16 able to be housed in the grooves 14A, 14B when the mold 1 is in the closed position as illustrated in FIG. 1A, so that the half shells and the base form a mechanical assembly that is non-deformable under the blow-molding pressure (of the order of 40×105 Pa). Arrangements of this type are represented, for example, in documents FR-2 720 680, FR-2 828 829 and FR-2 841 495.
It will be noted that, in the depiction of FIG. 1A, the plane of section of the closed mold 1 is substantially diametral and substantially parallel to the parting line 17 of the shells 10A, 10B.
In the configuration illustrated in FIG. 1A, the cavity portions 11A, 11B of the shells 10A, 10B occupy substantially the entire height of said shells 10A, 10B, which have a height substantially equal to that of the respective shell holders 9A, 9B, which is the height of the mold 1. Thus, the molding cavity 13 therefore has the maximum permissible height for this mold and corresponds to the maximum height of the containers that can be manufactured using this mold (for example 2-liter bottles, as illustrated).
In order to increase the production capability of the mold, it is desirable for it to be able to be configured for manufacturing not only said maximum-height containers, but also containers of lesser heights (for example 1-liter bottles, 0.6-liter bottles, etc.) which do, however, all have the same base. To these ends, it is known practice for the shells 10A, 10B equipped with the respective molding cavity portions 11A, 11B to be replaced by shells 20A, 20B provided with different respective molding cavity portions 19A, 19B (in this instance, molding cavity portions that are not as tall), as shown in FIG. 1B. The cavity portions 19A and 19B and the cavity portion 12 in the base together, when the mold is in the closed position, define a molding cavity 21 which is not as tall as the cavity 13 in FIG. 1A. In practice, the molding cavity portions 19A, 19B are positioned in the upper part of the half shells 20A, 20B, which are positioned at the tops of the shell holders. Thus, the overall layout of the molding device is maintained, with the mold holders 8A, 8B and the shell holders 9A, 9B and the base 5 also, provided that the axial positioning of this base with respect to the shells is altered to suit the reduction in height of the molding cavity portions.
The mold base 5 is supported by a mold base support 22 with which movement means (not shown in FIGS. 1A and 1B) able to move the mold base 5 axially during the molding process are associated. The mold base 5 is secured to the mold base support 22 by a connecting member. In this configuration, appropriate positioning of the mold base 5 with respect to the height of the molding cavity can be obtained by altering the height of the connecting member by changing this member (using a short connecting member 23 for the maximum-height molding cavity 13 as shown in FIG. 1A; and using a long connecting member 23′ for the molding cavity 21 of lesser height as shown in FIG. 1B) and/or by moving the mold base support 22 and the movement means associated with it.
These adjustments, however they are made, prove to be lengthy, restrictive and, ultimately, expensive. There is therefore, in practice, a pressing need to reduce or even eliminate these constraints.
Document U.S. Pat. No. 4,815,960 describes a molding device provided with a mold base the axial position of which can be adjusted by means of an axial threaded rod secured to the mold base by one of its ends. The threaded rod passes through an adjusting nut, supported such that it can turn freely by a fixed support, allowing the heightwise adjustment of the mold base. In this known arrangement, the adjusting nut is supported by means of a fixed bearing in which the nut is engaged and turns. The disadvantage with this solution lies in the fact that all the stresses that oppose the movement of the mold are borne at the interface between the rotary nut and the bearing: this results in wearing of the rubbing parts and a risk of the nut being torn out of the bearing.
So as to remedy to this problem, it could be provided to replace the rotary nut in said known structure with a fixed nut, particularly one secured to the frame, and then turn the threaded rod, the end of which would, on its transverse face, bear against the mold base. However, such an arrangement would in turn have a disadvantage which would be the wearing of the mold base in contact with the rotary transverse face of the threaded rod, or even possible deformation of the mold base resting against said small cross-section transverse face of the threaded rod.